on my road bike: clipless and I'll stay with it.
on my commuter: Campus Pedals from Performance Bike. SPD one side, flat the other side.
on my mountain bike: Flat pedals and a sturdy hiking shoe.
after years of spd pedals clogging with mud and my lack of technical skills I went to flat pedals. I climb just fine with them and ride all day on trails and dirt roads with them. Funny thing is the people I sometimes ride with, who are much better technical MTB'ers than I only noticed that I wasn't falling as much and took more risks on the MTB. I'm thinking of doing more long distance dirt road, fire road and double track journeys on this bike and don't know if I'll go back to clipless or not. It hasn't too noticeably affected my ability to climb.